The method and apparatus of this invention are ones relating to the cutting of pattern pieces from sheet material by means of a cutting tool moved along lines of cut defining the peripheries pattern pieces and wherein as the cutting tool is moved along such a peripheral line progress along the peripheral line is interrupted for the cutting of a slit notch with the tool being withdrawn from cutting engagement with the material as part of such slit notch cutting before being returned to the cutting of the peripheral line.
After pattern pieces are cut from sheet material they are removed either by hand or by machine from the adjacent waste material. To allow an efficient separation it is quite important that the pattern pieces be cleanly cut from the waste material and that no uncut strings, threads or connecting bridges exist between the pieces and the waste material. If such uncut features exist the involved pattern pieces may fail to be removed or expensive time consuminq additional manual steps may have to be performed to complete the separation. One way to eliminate, or at least reduce, this problem is to cut each pattern piece with a single complete movement of the cutting tool along the periphery of each pattern piece without removing it from start to finish from cutting engagement With the material. If the periphery of a pattern piece includes a sharp corner it is known, to avoid uncut threads and as described in U.S. Pat. No. 4,133,233, to cause the tool as it approaches the corner point to overcut, that is to cut beyond the corner point, before being withdrawn from the material, rotated and brought back to the corner point for further cutting along the peripheral line away from the corner point.
Slit notches may be cut in pattern pieces in various different ways as shown for example by U.S. Pat. No. 3,626,799; 3,766,813 and 1,667,553. In methods and apparatus shown by these patents clean cutting problems arising from slit notches are avoided by either cutting the notches after the peripheries of the pattern pieces have been gully cut or by non-withdrawal of the cutting tool during the cutting of a notch. The present invention, however, relates to situation where a notch is cut by the same knife as used to cut the periphery of a pattern piece with the notch being cut immediately upon the tool reaching a notch point during the cutting of the peripheral line and with the tool being withdrawn from cutting engagement with the material before returning to cutting of the peripheral line. The cutting tool is moved along the peripheral line of cut in cutting engagement with the material until reaching the point at which the slit is to occur. The tool is then moved inwardly in cutting engagement with the material relative to the pattern piece from the peripheral line of cut until reaching the inner end point of the slit. The tool is then withdrawn from cutting engagement with the work material and returned to coincidence with an already cut portion of the peripheral line near the notch point and then again moved forwardly along the peripheral line of cut. During cutting the tool exert forces on the material tending to displace or distort it from its neutral condition. When the tool is withdrawn from cutting engagement with the material, the material relaxes. Therefore, when the tool returns to the peripheral line the now relaxed material is likely to have a slightly different disposition on the supporting surface than when the tool first arrived at the notch point with the result that some threads or portions of the material may remain uncut as the cutting tool moves forwardly from the slit point along the peripheral line of cut if the tool is returned to cutting engagement with the material at exactly the notch point, as has heretofore been the case.
If the cutting tool is a knife reciprocated along an axis extending generally perpendicularly to the material being cut, such knife generally has a sharpened forward cutting edge, an unsharpened rear edge parallel to the forward edge and an inclined sharpened lower edge terminating in a lowermost point. The lowermost point may be either in line with the rear edge or in line with the sharpened forward edge depending on the direction of inclination of the sharpened lower edge. If the lowermost tip of the knife is in line with the rear edge the sharpened lower edge tends to generally face forwardly toward the uncut material as the knife is advanced forwardly along the line of cut. The force exerted on the material by the knife also tends to push the material forwardly. If the knife is withdrawn from the material the material tends to relax rearwardly. If the knife is now immediately returned to the material the generally forwardly facing inclined lower edge of the knife will tend to engage and cleanly cut the rearwardly displaced material since the inclined lower edge pushes such material forwardly against the adjacent body of uncut material to achieve a good cutting action. On the other hand, if the lower point of the knife is in alignment with the forward cutting edge the inclined lower sharpened edge faces generally rearwardly relative to the line of cut. If this blade is removed and re-inserted into the material during a cutting operation the portion of the material which relaxes rearwardly during the removal of the knife is, after re-insertion of the knife, engaged by the rearwardly facing lower inclined surface which tends to urge the material it engages rearwardly toward the already cut portion of the line. Therefore, there is no back-up material tending to resist rearward movement of the relaxed material with the result that such relaxed material may not be completely cut, particularly if he inclined lower edge of the knife is somewhat dull.
The general object of the invention is therefore to provide a method and apparatus for overcoming clean cutting problems of the type mentioned above arising from the Withdrawal of the cutting tool from the material when cutting slit notches in a pattern piece during the course of cutting the pattern piece periphery.
A more particular object of the invention is to provide a method and apparatus for eliminating or reducing clean cutting problems arising from slit notch cutting of the type referred to above regardless of whether the cutting tool is a knife with a generally forwardly facing lower edge or a knife with a generally rearwardly facing lower edge.
Other objects and advantages of the invention will be apparent from the following detailed description of a preferred embodiment and from the accompanying drawings and claims.